The present invention concerns circuits used for communication systems and pertains specifically to a low noise amplifier circuit with a phase matched switch topology.
Modern digital wireless systems, such as those used in cellular phones and local area networks (LANs) utilize signals with a frequency typically in the range of 0.5 gigahertz (GHz) to 6.0 GHz.
For strong transmission signals, for example when there is a relatively short transmission distance, it is often advantageous to use a switch or series of switches to bypass a microwave amplifier in order to conserve power and lower system gain. The microwave amplifier, while important to achieve high dynamic range for weak transmission signals, may be unnecessary for strong transmission signals. Providing a bypass of the microwave amplifier allows the system gain to be lowered when the input signal is strong.
U.S. Pat. No. 6,118,338 describes an amplifier with a switched bypass path where an R-C matching network in the bypass path matches the input and output impedance of the bypass path on the amplifier mode impedance. However, the circuit described in U.S. Pat. No. 6,118,338 does not make an attempt to match the S21 through phase of the bypass path to the S21 through phase in the amplifier mode. Some radio modulation schemes use the phase information of a signal to transmit data. In these phase modulated systems, it is desirable to maintain the same through phase when switching between the bypass path and the amplifier mode so the phase information is not lost during the path change.
In accordance with the preferred embodiment of the present invention, an amplifier and bypass switch circuit includes a circuit input, a circuit output, an amplifier and a switching circuit. The amplifier has an amplifier control input, and a first amplifier output. The amplifier control input is connected to the circuit input. The amplifier output is connected to the circuit output. The switching circuit includes a control input, a switch input, a switch output and a phase matching network. The switch output is connected to the circuit output. The switch input is connected to the circuit input. The phase matching network preserves phase information when the amplifier and bypass switch circuit switches between an amplifier mode and a bypass mode.